Question: Expand.
Answer: We expand the parentheses using the distributive property : $ A(B+C)= A\cdot B+ A\cdot C$ We can also think about the problem using an area model: $k^2$ $-4k$ $-5k^2$ Here's how the solution goes, algebraically: $\begin{aligned} &\phantom{=}{-5k^2}(k^2-4k) \\\\ &={-5k^2}(k^2)+({-5k^2})(-4k) \\\\ &=-5k^4+20k^3 \end{aligned}$ Here's how the solution looks in terms of the area model: $-5k^4$ $20k^3$ $k^2$ $-4k$ $-5k^2$ In conclusion, $-5k^2(k^2-4k)=-5k^4+20k^3$